


The Uncertainty Principle

by sevenofspade



Category: Young Avengers, Young Justice (Cartoon)
Genre: Choose Your Own Adventure, Gen, Physics
Language: English
Status: Completed
Published: 2014-12-06
Updated: 2014-12-06
Packaged: 2018-02-28 10:22:36
Rating: General Audiences
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 2,580
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/2728817
Author URL: https://archiveofourown.org/users/sevenofspade/pseuds/sevenofspade
Summary: <blockquote class="userstuff">
              <p>There's no such thing as "dead" when you're a physicist. Blame Schrödinger. Cassie and Wally certainly do.</p>
            </blockquote>





	The Uncertainty Principle

**Author's Note:**

> This contains a rather unseemly number of physics jokes and thoughts experiments.
> 
> It is also choose-your-own-adventure, because of quantum.

Who are you here for?  
I'm here for Cassie.  
I'm here for Wally.

  


* * *

  


Cassie Lang wakes up feeling like every bone in her body has been broken.

She gets up. She's a superhero, that's what superheroes do. Her vertebrae snap into place with a sickening pop. She stretches, settling her bones within her skin. 

Her surroundings are strange, like they bypass her eyes entirely to drop themselves fully fledged into her brain. It hurts her head. There's nothing for her to see — or not see, whatever — as far as she can tell.

She starts walking, picking a direction at random.

After a time, she comes across a person in old-fashioned clothes. They are quite pretty and wearing a man's suit in the style of the nineteenth century, but their hair is long and try as she might Cassie cannot tell what gender they are.

"Hello," Cassie says. "I'm Cassie."

They nod. "You may call me Maxwell, should you wish to call me anything."

"Where are we?" There is no ground beneath Cassie's feet.

"Celia calls this the Zone," Maxwell says. They smile. "I call it home."

"Celia?" The Zone sounds awfully populated for something without any material furnishings.

"We'll go see her as soon as we find the cat," Maxwell says.

As soon as Maxwell says that, something brushes against Cassie's legs. It's a cat, its fur colour hovering somewhere between white and black, neither wholly one nor the other, yet grey does not seem to fit. Either way, it purrs under her fingers when she reaches down to pet it.

She picks it up, holding it tightly against her chest. "Let's go."

Cassie still has no idea how Maxwell can tell which way is which, but they find Celia soon after. She's older than Cassie by a couple of years and dressed like an astronaut, with a French flag patch on her shoulder.

"Schrödinger!" Celia makes to take the cat from her as Cassie's world shatters.

She knows exactly where she is.

Cassie's story continues here.

  


* * *

  


Wally has no idea where he is, but he knows exactly how fast he's going.

As a physicist, he finds that hilarious. As the one trapped in some unknown place with no apparent way out, he finds it a bit distressing.

He picks a direction at random and runs. His surroundings still look the same.

He reaches Mach 1, 2, 5, 10, 25 and nothing changes. He keeps running faster.

He reaches escape velocity. On Earth, this is when there are some serious complications, like being hurled into space if you don't compensate.

Wally does not compensate.

His surroundings are still endless white as far as the eye can see and he does not feel gravity letting go of him anymore he previously felt gravity.

He keeps running, until a voice stops him short. "Well, that wasn't very smart, was it? What was it you were going do when you found yourself in space?"

Wally stops running. "Where did you come from?"

"Where did _you_ come from?" She's older than his grandmother, but Wally likes her.

"I was running," Wally says, "and now I'm here. No idea where here is. I'm Wally, by the way."

"Alice." She thinks for a moment. "By any chance, did you know exactly how fast you were running?"

"Yes! Are you a physicist?" You'd have to know at least something about physics to link his comment to Heisenberg.

She shakes her head. "No, but my sister is a spationaut."

"What's a spationaut?" It sounds cool, Wally thinks.

"Like an astronaut, but French. Maybe you've heard of her? Celia, yes, we're twins," she adds, even though Wally hasn't said anything. "Celia Langevin?"

The last name sounds familiar to Wally, but he doesn't know any French people. "Sorry, no. Do you think we could go see her?"

"Sure," Alice says and points behind him. "There she is."

Wally turns around to see a group of people comprising a tall scarecrow in a suit, a blonde girl his age holding a cat and a woman who looks exactly Alice, if Alice was seventy years younger.

Of course, the Langevin twins!

Wally's story continues here.

  


* * *

  


"None of you are real!" Wally throws up his hands.

"Wow," the girl says, "rude. I'm perfectly real, thank you."

"You might think you are," Wally says, but you're not."

"I assure you," Suit says, "Cassie is quite real. Those of us who are not are limited to the cat, for a given value of real."

"And you are?" Wally is on the defensive, for no good reason that he can see. Damn, but he hates this place.

"That's Maxwell," Cassie says. "Short for Maxwell's Demon, right?"

Maxwell nods. "The cat is named Schrödinger. It is not the first time we have had visitors from outside."

"Then how do we get out?" Cassie asks.

"Must we do everything for you?" Celia says, her lips curled back into a sneer. "Besides, none of us have any idea and we couldn't leave even if we wanted to."

They glare at each other in silence, until Cassie asks Wally, "Are you a superhero too?"

"Sort of," Wally says. "I used to be Kid Flash, but then I retired."

She sniffs. "Doesn't look like you're retired. Or is spandex civilian clothing in your universe?"

"Yeah, okay," Wally says, looking down at his suit, "I can see why you'd think that."

Cassie breathes in deep through her nose and holds out her hand to him. "Hi, I'm Cassie Lang, also known as the superhero Stature. Help me do science and get out of here?"

Wally agrees and they get down to business.

Cassie's Pym particles and Wally's Speed Force can be tied together just so...

"And then we'd get total waveform collapse!" Wally holds up his hand for a high-five.

Cassie jumps up to slap her hand against his. "With a complete harmonics resonance field! Wally, I think we're home free."

"Do you want to do the honours, or shall I?" Wally asks once they've set everything up.

"I'll do it," Cassie says and pulls the lever.

The story continues here.

  


* * *

  


The universe explodes inside her head and Cassie wakes.

She’s alone.  
She’s with Wally.

  


* * *

  


She wakes up alone.

She’s still in the Zone.  
She’s in her universe.  
She’s in Wally’s universe.

  


* * *

  


The ground is muddy beneath Cassie's body and there is a duck sitting on her chest. It quacks at her as she shoves in off. She gets herself to her feet.

She's in Central Park.

She's in Central Park and she can see the Baxter Building in the skyline. She's alive and she's home.

She can't see Wally. She hopes he's okay, because what else can she do?

She starts walking and then she starts running, in great loping bonds towards Avengers Mansion, hair free in the wind. She reaches the garden of the mansion and finds herself face to face with a statue of herself.

It's so weird, she looks nothing like she does in the mirror. Does her face really look like that? And her hair was never this straight, it's always had a light wave to it, unlike Kate's.

"Cassie?"

She turns around and there Kate is. She waves at her. "Hi."

Kate drops the wreath she was carrying and hugs Cassie, tears in both their eyes.

Meanwhile, Wally’s in his own universe.  
Meanwhile, Wally’s still in the Zone.

  


* * *

  


Cassie hates the snow. She hates this snow, at least. It doesn't snow like this is in New York so that means she's not home.

A blur of yellow zips past.

She calls out, "Wally?"

"It's Kid Flash, actually." The blur stops and he looks a bit like Wally, but he's shorter than her. "Do you know where Wally is? We detected Speed Force radiation so we thought he was here but he's not here -"

He's doing that motor-mouth thing that Tommy does when he's excited. Wally did that too, come to think of it. Is it a speedster thing?

"He was right behind me," Cassie says.

"Behind you where?" He's young, Cassie realises, maybe even younger than her.

"This going to sound weird," she starts.

A red blur draws up next to Kid Flash. That must be Flash Senior. "What is?"

"I think we were stuck in Physicsland," Cassie says. "Where you know exactly how fast you're going but you've no idea where you are!"

The two Flashes look at each other. "She's met Wally alright."

Like she couldn't have come up with that joke on her own. "You're like the cat in Schrödinger's box: you're both dead, alive and everywhere in the box."

Meanwhile, Wally’s still in the Zone.  
Meanwhile, Wally’s in Cassie’s universe.

  


* * *

  


Cassie wakes up with white burning on the inside of her brain.

She's still in the Zone, then. Ouch.

"Are you alright?" It's one of the Langevins. With her eyes closed, Cassie can't tell which.

"Yeah. Just give me a moment. What happened?" She opens her eyes. The white of the Zone is dim compared to the white painted inside her head.

"It didn't work," Celia says.

"I can see that," Cassie says. "Do you know what it was? That went wrong, I mean?"

"If we did," Maxwell says, "do you really think we would still be here? Do you think we want to be stuck here?"

"No," Cassie says, "but if you wanted to help, you only had to ask."

"I'm asking," Maxwell says. It doesn't sound like asking, more like demanding, but Cassie wants all the help she can get.

"Then let's get to work."

Meanwhile, Wally’s in his own universe.  
Meanwhile, Wally’s in Cassie’s universe.

  


* * *

  


Wally wakes up in Central Park. He can tell it's Central Park because that's what his visor display tells him. He can also tell Cassie isn't here. He hopes she's okay, wherever she is.

He's not in his universe. The map pinpointing his location doesn't have Gotham or Metropolis on it, even though it should.

He stretches and starts running to get his bearings.

Somewhere in the general vicinity of Greenland, someone catches up to him.

"Hi," the stranger says. "I'm Speed. And you are?"

"More imaginative," Wally says. "Codename's Kid Flash."

"Uh uh," Speed says.

"Wait," Wally says and stops running. "Speed. Tommy Shepherd?" He barrels on before the other speedster can answer, which is no easy feat. "Do you know a Cassie Lang — Stature?"

"You know Cassie? Where is she? Is she okay?" Tommy's words are blurring together like Bart's and Barry's. Why must Wally always be the slowest speedster, urgh.

"Yes, I don't know, last I saw her, yes," Wally says.

"Come on," Tommy says, "you gotta talk to Scott so he can work on getting her back."

  


* * *

  


Wally shakes the snow off himself. Cold. So cold. He really needs better thermal insulation in the suit. Or he could just get outta here.

Wally runs.

Then Wally runs into Kid Flash.

"I appreciate the sentiment," Kid Flash says, "but wow, that's in poor taste."

Wally knows that voice. "Bart?"

"Who are you?" Bart asks and Wally is proud that he didn't betray his secret identity.

"It's me," Wally says. "Wally?"

Bart's eyes narrow behind his mask. "Prove it."

"I know exactly how fast I'm going," Wally says with his most winning smile, "and I know exactly where I am!"

Bart laughs and hugs him. "No one else would make a joke this bad."

  


* * *

  


Maxwell is shaking Wally to wake him up.

"Ow," Wally says and Maxwell drops him. "Ow," Wally says again. He gets up and brushes invisible dust off himself. "Where's Cassie?"

Maxwell shrugs. "Out."

"Wow," Wally says, "that's very helpful."

"You're abandoning us like cowards and you expect us to be helpful?"

And yeah, okay, when it's put like that, Wally can understand why Maxwell's so pissed. "You want to get out? I thought you couldn't!"

"Doesn't mean we don't want to," Maxwell says.

"Do you," Wally swallows, feeling foolish and kind of like a dick, "want to work me with to get out?"

Maxwell smiles.

  


* * *

  


Where are Cassie and Wally?  
  
They're in Cassie’s universe.  
They're in Wally’s universe.  
They're in the Zone.

  


* * *

  


Cassie wakes up with Wally's weight pining her down. She pushes him off. His goggles fall off. He groans. Good. That means he's still alive.

She gets up and has to catch a tree to keep from falling down. Her legs feel like they're burning from the inside out and filled with cotton candy, all at once.

She prods Wally with the toe of her boot. "You okay?"

"I have the worse hangover," he says, "but other than that, yeah. Where are we?"

"Central Park, New York," Cassie says. "You can tell by the way no one cares we've just appeared out of thin air."

"Sounds like New York alright," Wally says and gets to his feet. He wobbles a little as he does.

"Come on," Cassie says, "I'm sure we can find someone to take you back to your home universe.

They do indeed find someone. Her name is America Chavez, she's a friend of Kate's and she can kick holes in the multiverse.

  


* * *

  


Wally crashes through the sound barrier and Cassie's awkward grip on his back sends him into a tailspin. They crash headfirst into a snowbank.

Wally gets up. "You okay?"

Cassie nods. "Did we make it?"

"I think so. Come on, let's go check." He picks her up, fireman-carry like, taking care not to jostle her ankle, since it looks bruised.

"Check New York first, please," she says, "we might be in my universe."

He doesn't think they are, but they might be and besides, there's a zeta tube in New York just like there is in Central City.

They've barely been in the city five seconds before Cassie says, "not my New York. It's missing the Baxter Building. You?"

Wally zips them to the nearest zeta tube. It is where it should be. "Looks like it. Only one way to find out for sure, though. Kid Flash. B03."

The door locks behind them, leaving them trapped in the cubicle. Cassie shrinks down, so she can be the unexpected ace up his sleeve in case of trouble.

Then Zatanna shows up and he does not need the ace up his sleeve. He waves Cassie a safe journey home over Zatanna's "Teg reh emoh efas dna elohw".

  


* * *

  


They wake up in the Zone with Cassie's brain trying to escape her skull through her eyes. She shakes Wally to wake him up.

"Did it work?" Wally staggers to his feet.

"No," Cassie says. She feels like screaming, like she's on fire, like each and every single one of her molecules is vibrating at an elevated pitch. Her heart is beating triple time against her ribs and her blood is thrumming in her veins, looking for an escape.

She feels like running.

She runs.

She runs and the world falls away beneath her feet, melting into a blur of white light.

She stops.

She's back next to Wally and he looks exactly the same, stupid look stuck on his face and all.

"Think big thoughts," she tells him.

He must listen to her, because suddenly he's twice her size. His voice is much too loud when he says, "what the hell."

"I think we switched powers," Cassie says. "We should get back to work. Maybe we can switch again or maybe we can go home. I can think of worse things than being a speedster."

**Author's Note:**

> The physics thought experiments referenced in this fic are:  
> \- [Heisenberg's Uncertainty Principle](http://en.wikipedia.org/wiki/Uncertainty_principle)  
> \- [Langevin's Twin Paradox](http://en.wikipedia.org/wiki/Twin_paradox)  
> \- [Maxwell's Demon](http://en.wikipedia.org/wiki/Maxwell%27s_demon)  
> \- [Schrödinger's Cat](http://en.wikipedia.org/wiki/Schr%C3%B6dinger%27s_cat)


End file.
